Based on how King's Fall took to be made and Luke Smith's discussions on the creative process behind Raids and their dev time, there's a very high chance that we won't see a Raid until Forge of the Gods and that Vex Void will have a Vex Arena, and not a Vex Raid. I'm personally fine with it, but thought this probability should be brought up and addressed so people don't flip their shit when Vex Void is finally announced.
http://m.ign.com/articles/2015/05/06/destiny-bungie-is-working-on-multiple-raids Development has been going on for Kings Fall and multiple other raids for a long time now. Plus community response to the arena was meh. Doubt it.